Method of using thermoelectric device

ABSTRACT

A method using an apparatus includes the following steps. Providing a thermoelectric composite material, and establishing a sufficient temperature gradient in the thermoelectric composite material to create a voltage. The thermoelectric composite material includes a carbon nanotube structure comprising a plurality of carbon nanotubes and a plurality of spaces defined by and between the carbon nanotubes, and an electrically conductive polymer layer coated on the carbon nanotube structure.

RELATED APPLICATIONS

This application is a continuation application of patent applicationSer. No. 12/592,903 filed on Dec. 3, 2009 from which it claims thebenefit of priority under 35 U.S.C. 120. This application claims allbenefits accruing under 35 U.S.C. §119 from China Patent Application No.200910108234.7, filed on Jun. 19, 2009 in the China IntellectualProperty Office.

BACKGROUND

1. Technical Field

This disclosure relates to a method of using a thermoelectric deviceincluding carbon nanotube (CNT) based thermoelectric material.

2. Description of Related Art

The thermoelectric effect is the direct conversion of temperaturedifferences to electric voltage and vice versa. A thermoelectricmaterial creates a voltage when there is a temperature gradient.Conversely when a voltage is applied to the thermoelectric material, itcreates a temperature gradient (known as the Peltier effect). At atomicscale (specifically, charge carriers), an applied temperature gradientcauses charged carriers in the material, whether they are electrons orelectron holes, to diffuse from the hot side to the cold side, similarto a classical gas that expands when heated; hence, thethermally-induced current. Seebeck coefficient of a thermoelectricmaterial measures the magnitude of an induced thermoelectric voltage inresponse to a temperature difference across that material.

The performance of thermoelectric devices is quantified by a figure ofmerit, given by ZT=S²σT/κ, where S, σ, T and κ are, respectively, theSeebeck coefficient, electrical conductivity, absolute temperature andthermal conductivity. Since Seebeck coefficient S has the squarerelation to the ZT value, indicating the ability of conversion betweenheat and electrical power, increasing the value of Seebeck coefficientis an effective way to enlarging the figure of merit of thermoelectricmaterials.

During the past years, great efforts have been taken to increase theefficiency of heat-power conversion. Various promising approaches havebeen explored to improve the figure of merit value, involvingquantum-well structures, crystals with complex electronic structures,thin and multilayer films, the so-called phonon-glass/electron-crystalcompound materials and so on. Among them, composites were considered notto provide any benefit because it was determined and reported that thefigure merit of composites could not be any higher than the maximum oneof its components through theoretical numerical simulation (I. Webman,J. Jortner, M. H. Cchen, Phys. Rev. B 1977, 16, 2959.).

What is needed, therefore, is to provide a method of using a deviceincluding thermoelectric composite material with a high efficiency ofheat-power conversion.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referencesto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a schematic structural view of an embodiment of athermoelectric composite material including disordered CNTs.

FIG. 2 is a scanning electron microscope (SEM) image of an embodiment ofa′ thermoelectric composite material including disordered CNTs.

FIG. 3 is a cross-sectional view of a device used for measuring Seebeckcoefficients of the thermoelectric composite material.

FIG. 4 displays distribution of Seebeck coefficients of thethermoelectric composite martial, a flocculated CNT film and apolyaniline sheet under different pressures.

FIG. 5 is a schematic structural view of another embodiment of athermoelectric composite material including ordered CNTs.

FIG. 6 is a schematic structural view of an embodiment of athermoelectric composite material including a CNT array.

FIG. 7 displays distribution of Seebeck coefficients of thethermoelectric composite martial, a CNT array and a polyaniline sheet,under different pressures.

FIG. 8 displays a thermoelectric device using the thermoelectriccomposite materials.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1 and FIG. 2, an embodiment of a thermoelectriccomposite material 10 includes a CNT structure 16 and an electricallyconductive polymer layer 14. The CNT structure 16 works as a framework.The electrically conductive polymer layer 14 is coated on the surfacesof the CNT structure 16. That is, the electrically conductive polymerlayer 14 is supported by the CNT structure 16.

The CNT structure 16 includes a plurality of CNTs 12 and spaces 18. Theplurality of CNTs 12 is assembled together by Van der Waals attractiveforces. The spaces 18 are formed between the adjacent CNTs 12 of the CNTstructure 16. A size of each space 18 can be in a range from about 50nanometers to about 500 nanometers. The size of the space 18 representsthe maximum distance between two points on the space 18. Thethermoelectric composite material 10 includes a plurality of spaces 18.

The electrically conductive polymer layer 14 is coated on the spaces18CNT structure 16. The electrically conductive polymer layer 14 wrapsaround the CNTs 12 to form a tubular coating layer structure. Here, theindividual CNT 12 and the CNT structure 16 serve as the core and thetemplate. In one embodiment, the electrically conductive polymer layer14 is disposed on the whole surface of the CNT structure 16, which meansthat the surface of each CNT 12 is coated by the electrically conductivepolymer layer 14.

Further, the CNTs 12 in the CNT structure 16 can be arranged orderly ordisorderly. The term ‘disordered CNT structure’ includes, but is notlimited to, a structure where the CNTs are arranged along many differentdirections so that the number of CNTs arranged along each differentdirection can be almost the same (e.g. uniformly disordered); and/orentangled with each other. ‘Ordered CNT structure’ includes, but is notlimited to, a structure where the CNTs are arranged in a consistentlysystematic manner, e.g., the CNTs are arranged approximately along asame direction and or have two or more sections within each of which theCNTs are arranged approximately along a same direction (differentsections can have different directions). In one embodiment, the CNTstructure 16 includes a plurality of CNTs 12 arranged disorderly.

The CNTs 12 in the CNT structure 16 can be single-walled, double-walled,and/or multi-walled CNTs. It is also understood that the CNT structure16 may comprise of many layers of ordered and/or disordered CNT films.Each layer of the ordered and/or disordered CNT films is coated with oneelectrically conductive polymer layer 14.

In one embodiment, the CNT structure 16 is a disordered CNT structureincluding a flocculated CNT film. The flocculated CNT film can include aplurality of long, curved, disordered CNTs entangled with each other.The length of the CNTs in the film can be greater than 10 centimeters.Furthermore, the flocculated CNT film can be isotropic. The CNTs can besubstantially uniformly dispersed in the CNT film. The adjacent CNTs areacted upon by the van der Waals attractive force therebetween, therebyforming an entangled structure with spaces defined therein. If there ismore than one flocculated CNT film, the electrically conductive polymerlayer 14 is coated on each one of the flocculated CNT film.

The flocculated CNT film is very porous. Sizes of the spaces can be lessthan 10 micrometers. The porous nature of the flocculated CNT film willincrease specific surface area of the CNT structure. Further, due to theCNTs in the CNT structure being entangled with each other, the CNTstructure employing the flocculated CNT film has excellent durability,and can be fashioned into many desired shapes with a low risk to theintegrity of CNT structure. Thus, the CNT structure may be formed intomany shapes. The flocculated CNT film, in some embodiments, will notrequire the use of structural support due to the CNTs being entangledand adhered together by van der Waals attractive force therebetween. Thethickness of the flocculated CNT film can range from about 0.5nanometers to about 1 millimeter. It is also understood that many of theembodiments of the CNT structure are flexible and/or do not require theuse of structural support to maintain their structural integrity.

A material of the electrically conductive polymer layer 14 can bepolyaniline, polypyrrole, polythiophene, polyacetylene,polyparaphenylene, poly phenylene vinylene, or any combination thereof.A thickness of the electrically conductive polymer layer 14 is fromabout 30 nanometers to about 90 nanometers. A weight percentage of theelectrically conductive polymer layer 14 in the thermoelectric compositematerial 10 is in a range from about 5% to about 80%. In one embodiment,the material of the electrically conductive polymer layer 14 ispolyaniline, and the weight percentage of the electrically conductivepolymer layer 14 in the thermoelectric composite material 10 is in arange from about 5% to about 20%.

Referring to FIG. 3, a Seebeck coefficient measuring device 100 includesa first element 102 and a second element 103. Two thermocouples 107 areseparately located on the two opposite surfaces of the first and secondelements 102, 103. The first element 102 is cooled by a circulatingliquid cooling device 104. The second element 103 is heated by aconstant current constant voltage source 105. In one embodiment, thefirst element 102 and the second element are copper blocks, thethermoelectric composite material 10 is cut into round sheets. The roundsheet has a diameter of 13 millimeters, a thickness of 55 microns and aweight of 3.95 milligrams.

The thermoelectric composite material 10 with a shape of round sheet canbe located between the first and second elements 102, 103. A pressure isapplied on the first and second elements 102, 103, which places thethermoelectric composite material 10 in substantially full contact withthe first and second elements 102, 103. In one embodiment, thetemperature of the first copper block 102 is maintained in a range fromabout 17° C. to about 19° C. via the circulating liquid cooling device104. The temperature of the first copper block 103 is maintained in arange from about 47° C. to about 49° C. via the constant currentconstant voltage source 105.

The temperature difference (ΔT) is measured via the two thermocouples107 attached to the first and second elements 102, 103 on either side ofthe sheet of the thermoelectric composite material 10, respectively. Thepotential difference (ΔV) is measured by a nanovoltmeter (not shown)with two copper branches welding the first and second elements 102, 103,respectively. The temperature and potential differences aresimultaneously measured, so the Seebeck coefficient at temperatureT=(T₁+T₂)/2 can be obtained by S=ΔV/ΔT. The Seebeck coefficient of aflocculated CNT film and a polyaniline sheet is measured via the samemethod as described above.

Referring to FIG. 4, it is noted that the Seebeck coefficient of thethermoelectric composite material 10 is far greater than that of theflocculated CNT film and that of the polyaniline sheet. For thethermoelectric composite material 10 employing a flocculated CNT filmand a polyaniline sheet as the conductive polymer, an enhancement of20.4% were observed over any of the parts. Since Seebeck coefficient hasthe square relation to the Z value, indicating the ability of conversionbetween heat and electrical power, our approach would be a possible andeffective way to enlarging the figure of merit of the thermoelectricmaterials 10. Thus the thermoelectric composite material 10 has a highefficiency of heat-power conversion.

While it is not totally clear why this composite has this effect, it isbelieved that the reason for the Seebeck coefficient enhancement is asfollows. One-dimension nanoscale material was considered to have betterthermoelectric properties than 2D or 3D ones. There is believed to be amuch higher density of states at Fermi level in low-dimensionstructures. Conducting polymers are also usually referred to 1D materialas CNTs. So the carriers are confined along the polymer chains and thetube axis, respectively. While in the pure PANI, polymer chains easilygathered in the form of short bars or clusters, so 1D character wasunconspicuous. Using the novel method described here, polyanilinecoatings can grow gradually around the CNT template. The thinpolyaniline layer coating CNTs constitute a freestanding network and thenanowires preferably lie down in the plane perpendicular to thicknessdirection. When a carrier transported from a CNT coated polyaniline toanother one, it would pass through a CNT/polyaniline interface and athin polyaniline layer. So lots of barriers in the form of interfaceswould exist through the transport along the thickness direction. Here aphenomena called energy-filtering effect (i.e., appropriate potentialbarriers at crystallite boundaries restrict the carriers with lowerenergy than the barrier height entering a material, while allowing theones with a higher mean energy substantially passing through theinterface preferentially) may arise, thereby increasing the mean carrierenergy in the flow, hence, the Seebeck coefficient.

Referring to FIG. 5, one embodiment of a thermoelectric compositematerial 20 includes a CNT structure 26 and an electrically conductivepolymer layer 24. The CNT structure 26 is a Ordered CNT structureincluding a plurality of spaces 28 and CNTs 22. The CNTs 22 are arrangedorderly in the CNT structure 26. The plurality of spaces 28 is formedbetween the adjacent CNTs 22 in the CNT structure 26. A size of thespaces 28 is in a range from about 50 nanometers to about 500nanometers. The electrically conductive polymer layer 24 is disposed onthe whole surface of the CNT structure 26, which means that the surfaceof each CNTs 22 is coated by the electrically conductive polymer layer24. The CNT structure 26 can include at least one drawn CNT film. Thedrawn CNT film includes a plurality of successive and oriented CNTsjoined end-to-end by van der Waals attractive force therebetween. Thedrawn CNT film can be formed by drawing a film from a CNT array that iscapable of having a film drawn therefrom. The drawn CNT film includes aplurality of spaces formed between the adjacent CNTs in the drawn CNTfilm. The CNT structure 16 can also include at least two stacked drawnCNT films. An angle α between the preferred orientation of the CNTs inthe two adjacent CNT films is in a rang from about 0 degrees to about 90degrees.

The CNT structure 26 can also include at least one pressed CNT film. TheCNTs in the pressed CNT film are arranged along a same direction orarranged along different directions. The CNTs in the pressed CNT filmcan be overlapped with each other. The adjacent CNTs are combined andattracted by van der Waals attractive force. An angle between a primaryalignment direction of the CNTs and a base of the pressed CNT film suchthat the angle is in a range from about 0 degrees to about 15 degrees.The pressed CNT film can be formed by pressing a CNT array. The angle isclosely related to pressure applied to the CNT array. The greater thepressure is, the smaller the angle is. The CNTs in the pressed CNT filmcan parallel to the surface of the pressed CNT film when the angle is 0degrees. A length and a width of a single pressed CNT film is determinedby the size of the array.

Referring to FIG. 6, another embodiment of a thermoelectric compositematerial 30 includes a CNT structure 36 and an electrically conductivepolymer layer 34. The CNT structure 36 includes a plurality of CNTs 32and a plurality of spaces 38 defined by and between the CNTs 32. The CNTstructure 36 is an array. The electrically conductive polymer layer 34is coated on the surface of the CNTs 32.

Referring to FIG. 7, it demonstrates that the Seebeck coefficient of thethermoelectric composite material 30 is far greater than the CNT arrayand the polyaniline sheet. Thus the thermoelectric composite material 30has a high efficiency of heat-power conversion.

Referring to FIG. 8, one embodiment of a thermoelectric device 40comprises a first element 402, a second element 403, two electrodes 407and a thermoelectric composite material 40. The thermoelectric compositematerial 40 is sandwiched between the first element 402 and the secondelement 403. Two electrodes 407 are separately located on the two facedsurfaces of the thermoelectric composite material 40. The thermoelectriccomposite material 40 can be same as the thermoelectric compositematerial 10, 20, 30. The thermoelectric composite material 40 produces avoltage when there is a sufficient temperature difference between thefirst element 402 and the second element 403.

The first element 402 is one heat source with high temperature. Thesecond element 403 is another heat source with a low temperature. Thus,a temperature difference is achieved between the two faced surfaces ofthe thermoelectric composite material 40. A voltage can be outputted viathe two electrodes 407 separately connected with the two faced surfacesof the thermoelectric composite material 40.

One embodiment of a method of using the thermoelectric device 400includes:

-   -   providing a thermoelectric composite material 40, the        thermoelectric composite material 40 comprising:        -   a carbon nanotube structure comprising a plurality of carbon            nanotubes and a plurality of spaces defined between the            carbon nanotubes; and        -   an electrically conductive polymer layer coated on the            carbon nanotube structure; and    -   achieving a sufficient temperature gradient in the        thermoelectric composite material to create a voltage.

In another embodiment, the method of using the thermoelectric device 400comprises of:

-   -   providing a thermoelectric composite material 40, the        thermoelectric composite material 40 comprising:        -   a plurality of carbon nanotubes joined together by van der            Waals attractive forces to form a carbon nanotube structure;        -   a plurality of spaces; and        -   an electrically conductive polymer layer, wherein the            electrically conductive polymer layer wraps around the            carbon nanotubes to form a tubular coating layer structure,            and each of the plurality of carbon nanotubes and the carbon            nanotube structure serve as a core and a template,            respectively; and    -   achieving a sufficient temperature gradient in the        thermoelectric composite material to create a voltage.

In yet another embodiment, the method of using the thermoelectric device400 comprises of:

-   -   providing the thermoelectric device 400 comprising:        -   two electrodes 407;        -   a first element 402;        -   a second element 403; and        -   a thermoelectric composite material 40 sandwiched between            the first element and the second element, the thermoelectric            composite material 40 comprising:            -   a carbon nanotube structure comprising a plurality of                carbon nanotubes and a plurality of spaces defined by                and between the carbon nanotubes; and            -   an electrically conductive polymer layer coated on                surfaces of the carbon nanotubes;    -   achieving a temperature difference between the first element 402        and the second element 403; and    -   outputting a voltage via two electrodes 407.

In one embodiment, the temperature difference in or between the twosurfaces of the thermoelectric composite material 40 is at least 30° C.

In some embodiments, the thermoelectric composite material 40 is locatedbetween the first and the second element, 402, 403. In one embodiment,the first element 402 can have a temperature from about 47° C. to about79° C., and the temperature of the second element 403 can be in a rangefrom about 17° C. to about 19° C. The temperature difference between thetwo faced surfaces of the thermoelectric composite material can be in arange from about 30° C. to about 60° C. In another embodiment, thetemperature of the first element 402 is 47° C., the temperature of thesecond element 403 is 17° C.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the disclosure. Variations maybe made to the embodiments without departing from the spirit of thedisclosure as claimed. The above-described embodiments illustrate thescope of the disclosure but do not restrict the scope of the disclosure.

1. A method, the method comprising: providing a thermoelectric compositematerial, the thermoelectric composite material comprising: a carbonnanotube structure comprising a plurality of carbon nanotubes and aplurality of spaces defined between the carbon nanotubes; and anelectrically conductive polymer layer coated on the carbon nanotubestructure; generating a current by establishing a sufficient temperaturegradient in the thermoelectric composite material.
 2. The method ofclaim 1, wherein the carbon nanotube structure supports the electricallyconductive polymer layer.
 3. The method of claim 2, wherein the carbonnanotubes are held together by van der Waals attractive forces.
 4. Themethod of claim 1, wherein the electrically conductive polymer layer iscoated on inside surfaces of the spaces.
 5. The method of claim 1,wherein the spaces are micropores and a size of each of the microporesis in a range from about 50 nanometers to about 500 nanometers.
 6. Themethod of claim 3, wherein the carbon nanotubes are entangled with eachother.
 7. The method of claim 1, wherein the carbon nanotube structurecomprises a flocculated carbon nanotube film, the flocculated carbonnanotube film comprises a plurality of curved and disordered carbonnanotubes entangled with each other.
 8. The method of claim 3, whereinat least one section of the carbon nanotube structure has a portion ofthe carbon nanotubes arranged substantially along a same direction. 9.The method of claim 8, wherein the carbon nanotube structure comprisesat least one drawn carbon nanotube film.
 10. The method of claim 8,wherein the carbon nanotube structure is a carbon nanotube array. 11.The method of claim 1, wherein a material of the electrically conductivepolymer layer comprises of a material that is selected from a groupcomprising polyaniline, polypyrrole, polythiophene, polyacetylene,polyparaphenylene, poly phenylene vinylene, and combinations thereof.12. The method of claim 11, wherein the material of the electricallyconductive polymer layer is polyaniline, the weight percentage of thepolyaniline in the thermoelectric composite material is in a range fromabout 5% to about 20%.
 13. A method comprising: providing athermoelectric composite material, the thermoelectric composite materialcomprising: a plurality of carbon nanotubes joined together by van derWaals attractive forces to form a carbon nanotube structure; a pluralityof spaces; and an electrically conductive polymer layer, wherein theelectrically conductive polymer layer wraps around the carbon nanotubesto form a tubular coating layer structure, and each of the plurality ofcarbon nanotubes and the carbon nanotube structure serve as a core and atemplate, respectively; and achieving a sufficient temperature gradientin the thermoelectric composite material to create a voltage.
 14. Themethod of claim 13, wherein the plurality of spaces is formed betweenadjacent carbon nanotubes.
 15. The method of claim 14, wherein a size ofeach of the spaces is in a range from about 50 nanometers to about 500nanometers.
 16. The method of claim 14, wherein the carbon nanotubestructure comprises a flocculated carbon nanotube film, the flocculatedcarbon nanotube film comprises a plurality of curved and disorderedcarbon nanotubes entangled with each other.
 17. The method of claim 13,wherein a thickness of the electrically conductive polymer layer is in arange from about 30 nanometers to about 90 nanometers.
 18. A method, themethod comprising: providing an apparatus comprising: two electrodes; afirst element; a second element; and a thermoelectric composite materiallocated between the first element and the second element, thethermoelectric composite material comprising: a carbon nanotubestructure comprising a plurality of carbon nanotubes and a plurality ofspaces defined by and between the carbon nanotubes; and an electricallyconductive polymer layer coated on surfaces of the carbon nanotubes;achieving a temperature difference between the first element and thesecond element; and outputting a voltage via the two electrodes.
 19. Themethod of claim 18, wherein the temperature difference between the firstelement and the second element is at least 30 degrees.